radiator reserior cap blowed off
 

while sitting in drive thru while idle my 05 radiator reservoir cap had blown off, thought it was a hose busted. it never ran hot I immediatly pulled over lost a little antifreeze. The day before while idle I could smell antifreeze but just pulled off and it ran fine went about fifty miles, no other problems. Can anybody tell me what to look for? Only had car about a month if that. My first Mini Cooper.:confused:
Thanks